The present invention relates to a rolling bearing unit having a rotating speed detector for rotatably supporting a wheel of an automobile by a suspension, and the rolling bearing unit having a rotating speed detector is used for detecting a rotating speed of the wheel.
A rolling bearing unit having a rotating speed detector is used for rotatably supporting a wheel of an automobile by a suspension and also used for controlling an anti-lock brake system (ABB) or a traction control system (TCS) by detecting a rotating speed of the wheel with the detector. Conventionally, various types of rolling bearing units having rotating speed detectors are well known. Each rotating speed detector incorporated into the rolling bearing unit includes a tone wheel, which is an element to be detected, rotated in conjunction with a wheel, and a sensor to output an output signal, the frequency of which changes in proportion to a rotating speed of the tone wheel. For example, a rolling bearing unit having a rotating speed detector shown in FIGS. 19 and 20 is described in the Technical Report No. 94-16051 by HATSUMEI KYOKAI, which is referred to as the first conventional example, hereinafter.
A hub 1 includes an inner race assembly. A flange 2 for fixing a wheel is formed on an outer circumferential surface of the outside end portion of the hub 1. The outside is defined as a side located outside of a vehicle with respect to the width direction of the vehicle when the rolling bearing is assembled into the vehicle. An inner raceway 3a and a step portion 4 are formed on an outer circumferential surface of the middle portion of the hub 1. Further, an inner raceway 3b is formed on an outer circumferential surface of the hub 1. In this way, an inner race 5 composing the inner race assembly in conjunction with the hub 1 is supported while an outer end surface of the inner race 5 is pushed against the step portion 4. In this connection, instead of directly forming the inner raceway 3a on the outer circumferential surface of the hub 1, another inner race (not shown) different from the hub 1 may be provided, and the inner race and the above inner race 5 may be outwardly engaged with the hub 1 so as to be fixed.
A male screw portion 6 is formed in a portion close to the inside end of the hub 1. The inside is defined as a side located inside of a vehicle with respect to the width direction of the vehicle when the rolling bearing is assembled into the vehicle. When a nut 7 is fastened to the male screw 6, the inner race 5 is fixed in a predetermined portion on the outer circumferential surface of the hub 1, so that the inner race assembly can be composed. An attaching portion 9 for fixing the outer race 8 to the suspension is formed on an outer circumferential surface of an outer race 8 arranged around the hub 1. Outer raceways 10a, 10b are formed on an inner circumferential surface of the outer race 8. The outer raceways 10a, 10b are respectively opposed to the inner raceways 3a, 3b. A plurality of rolling elements 11, 11 are installed between the inner raceways 3a, 3b and the outer raceways 10a, 10b. Due to the above arrangement, the hub 1 is capable of rotating inside the outer race 8. In this connection, in the example shown in FIGS. 19 and 20, balls are used for the rolling elements. However, in the case of a rolling bearing unit used for an automobile to which a heavy load is given, tapered rollers are used as the rolling elements in some cases. A seal ring 12 is fitted between the inner circumferential surface of the outside end portion of the outer race 8 and the outer circumferential surface of the hub 1. Since the seal ring 12 is arranged between the inner circumferential surface of the outer ring 8 and the outer circumferential surface of the hub 1, an outside and opening of the space in which the plurality of rolling elements are arranged is closed by the seal ring 12.
A base end portion of the tone wheel 13, that is, a left end portion of the tone wheel 13 shown in FIGS. 19, 20 is engaged with and fixed to and inside end portion of the inner race 5 which is a little distant from the inner raceway 3b. The entire tone wheel 13 is formed from a magnetic metal sheet such as a steel sheet into an annular shape (a short cylindrical shape). The tone wheel 13 is composed of a small diameter portion 14 and a large diameter portion 15 which are continuously connected to each other by a step portion 16, in which the small diameter portion 14 and the large diameter portion 15 are formed concentrically. The large diameter portion 15 of the tone wheel 13 is outwardly engaged with the outer circumferential surface of the end portion of the inner race 5, and the step portion 15 comes into contact with an end edge of the inner race 5. Under the above condition, the tone wheel 13 is supported by and fixed to the inner race 5. Therefore, the small diameter portion 14 is supported concentrically with the inner race 5. A plurality of through-holes 17 are formed in the small diameter portion 14 of the tone wheel 13 to serve as cutout portions on the rotational side. These through-holes 17 are formed in the circumferential direction at regular intervals. Accordingly, the magnetic characteristic of the tone wheel 13 is alternately changed in the circumferential direction at regular intervals. Shapes of the through-holes 17 are the same. Each through-hole 17 is formed into a rectangle, the long side of which is disposed in the axial direction, that is, the transverse direction in FIGS. 19 and 20.
An inside end opening of the outer race 8 is closed by a cover 18 formed into a cylindrical shape having a bottom from a metal sheet such as a stainless steel sheet or an aluminum alloy sheet by means of drawing. An annular synthetic resin member 21 which embeds an annular sensor 20 is fitted on an inner circumferential side of the cylindrical portion 19 composing the cover 18. The annular sensor 20 includes: a permanent magnet 22; a stator 23 composed of a magnetic member such as a steel sheet; and a coil 24. When these members 22, 23, 24 are embedded in the above synthetic resin 21, they are entirely formed into an annular shape.
In the above components of the sensor 20, the permanent magnet 22 is formed into an annular shape (ring shape) and magnetized in the diametrical direction. An inner circumferential surface of the permanent magnet 22 is opposed to a base end portion of the small diameter portion 14 of the tone wheel 13 while a minute clearance 25 is maintained between them. An outer circumferential surface of the portion of the tone wheel 13 in which the through-hole 17 is not formed is opposed to a base and portion of the small diameter portion 14 of the tone wheel 13 while a minute clearance is maintained between them. The stator 23 is entirely formed into an annular shape, the section of which is a substantial J-shape. An inner circumferential surface of the end portion of the outer diameter side cylindrical portion 26 composing the stator 23 is arranged close to or contacted with an outer circumferential surface of the permanent magnet 22. An inner circumferential surface of the inner diameter side cylindrical portion 27 composing the stator 23 is opposed to a portion of the tone wheel 13 in which the plurality of through-holes are formed. In the inner diameter side cylindrical portion 27, a plurality of cutout portions 28, which are stationary side cutout portions, are formed at regular intervals (central angle pitch), which are the same as those of the through-holes 17, in the circumferential direction of the inner diameter side cylindrical portion 27. Accordingly, the inner diameter side cylindrical portion 27 is formed into a comb-shape.
The coil 24 is formed into an annular shape in such a manner that a wire is wound around a bobbin made of nonmagnetic material. The coil 24 is arranged in a portion of the inner circumferential side 26 of the outer diameter side cylindrical portion 26 composing the stator 23. An electro-motive force generated in the coil 24 is taken out from a connector 30, which is a signal taking means, protruding from an outer surface of the cover 18.
In the rolling bearing unit having a rotating speed detector composed in the above manner, when the tone wheel 13 is rotated together with the hub 1, the magnetic flux density in the stator 23 opposed to the tone wheel 13 is changed, and the voltage generated in the coil 24 is changed at the frequency proportional to the rotating speed of the hub 1. The principle in which the voltage generated in the coil 24 is changed in accordance with a change in the magnetic flux flowing in the stator 23 is the same as the principle of the conventionally well known sensor used for detecting a rotating speed. The reason why the density of magnetic flux flowing in the stator 23 is changed in accordance with the rotation of the tone wheel 13 is described as follows.
Intervals of the plurality of through-holes 17 provided in the tone wheel 13 are the same as those of the cutout portions 28 provided in the stator 23. Accordingly, when the tone wheel 13 is rotated, each through hole 17 is opposed to each cutout portion 28 all over the circumference at one moment. At this moment when each through-hole 17 is opposed to each cutout portion 28, a pillar portion, which is a magnetic body, provided between the through-holes 17 adjacent to each other is opposed to a tongue member, which is a magnetic body, provided between the cutout portions 28 adjacent to each other. Under the condition that each pillar portion, which is a magnetic body, is opposed to each tongue member, which is also a magnetic body, a magnetic flux of high density flows between the tone wheel 13 and the stator 23.
On the other hand, when the phase of the through-hole 17 deviates from the phase of the cutout portion 28 by half the interval, the density of magnetic flux flowing between the tone wheel 13 and the stator 23 is lowered. In the above condition, the through-hole 17 provided in the tone wheel 13 is opposed to the tongue member, and at the same time the cutout portion 28 provided in the stator 23 is opposed to the pillar portion. A relatively large space between the tone wheel 13 and the stator 23 is formed all over the circumference under the above condition in which the pillar portion is opposed to the cutout portion 28 and the tongue member is opposed to the through-hole 17. Under this condition, the density of magnetic flux flowing between both members 13 and 23 is lowered. As a result, a voltage generated in the coil 24 is changed in proportion to the rotating speed of the hub 1. Due to the above action, the sensor 20 changes an output voltage generated in the coil 24 at the frequency proportional to the rotating speed of the hub 1.
However, in the rolling bearing unit having a rotating speed detector according to the first conventional example, the following problems may be encountered. In the first conventional example shown in FIGS. 19 and 20, the synthetic resin 21 in which the sensor 20 is embedded and the synthetic resin composing the connector 30 are disposed on both sides of the cover 18 made of a metallic sheet. Accordingly, the manufacturing work is complicated, and the cost is raised. That is, the rolling bearing unit having a rotating speed detector shown in FIGS. 19, 20 is manufactured as follows. First, the sensor 20 is embedded in the synthetic resin 21, and then the synthetic resin 21 is provided inside the cover 18. After that, under the condition that the cover 18 is set in the mold, injection molding is conducted to form the connector 30. Therefore, it is necessary to conduct the injection molding process twice. Alternatively, it is necessary to provide an adhesion process in which the synthetic resin 21 and the connector 30, which have been made by means of injection molding, are made to adhere to each other. As a result, the manufacturing cost is raised.
FIG. 21 is a view showing a rolling bearing unit having a rotating speed detector according to the second conventional example disclosed in Unexamined Japanese Patent Publication No. 63-166601.
The rotating wheel is composed of a hub 1 and an inner race 2. A flange 3 for fixing a wheel is formed in the outside end portion of the hub 1. An inner raceway 4a is formed in an outer circumferential surface of the middle portion of the hub 1. An inner raceway 4b is formed on an outer circumferential surface of the inner race 2. The inner race 2 is outwardly engaged with an outer circumferential surface of the middle portion of the hub 1. A male screw portion 5 is formed on an outer circumferential surface of the inside end portion of the hub 1. The male screw portion 5 is screwed to a nut 6. When the nut 6 is screwed to the male screw portion 5, an inside end surface of the inner race 2 is pushed, so that the inner race 2 can be fixed at a predetermined position on the outer circumferential surface of the hub 1.
A flange-shaped attaching portion 8 for supporting a suspension (not shown) is formed on an outer circumferential surface of the outer race 7 which is a stationary wheel. Two rows of outer raceways 9a, 9b are formed on an inner circumferential surface of the outer race 7. A plurality of rolling elements 10, 10 are formed between the outer raceways 9a, 9b and the inner raceways 4a, 4b. In this arrangement, the hub 1 is rotatably supported inside the outer race 7 supported by the suspension via the attaching portion 8.
The nut 6 includes a disk-shaped rotor 11. An irregular portion 12 is formed on the inside surface of the rotor 11. By the action of the irregular portion 12, the nut 6 generates a pulse-like output in a sensor 14 described later in accordance with the rotation of the hub 1. That is, the nut 6 functions as a tone wheel. A cover 13 is engaged with the inside opening of the outer race 7. The sensor is fixed to the cover 13, and an outside end surface of the sensor 14 is opposed to the irregular portion 12.
In the rolling bearing unit having a rotating speed detector described above, a wheel fixed to the flange portion 3 arranged in the outside end portion of the hub 1 can be rotatably supported by the suspension which holds the outer race 7. When the rotor 11 integrated with the nut 6 screwed to the inside end portion of the hub 1 is rotated in accordance with the rotation of the wheel, an output of the sensor 14 opposed to the irregular portion on the inside surface of the rotor 11 is changed. The frequency of a change in the output of the sensor 14 is proportional to the rotating speed of the wheel. Accordingly, when the output signal of the sensor 14 is inputted into a controller not shown in the drawing, it is possible to fince the rotating speed of the wheel. Therefore, ABS and TCS can be appropriately controlled.
In the conventional rolling bearing unit having a rotating speed detector composed as described above, an outside opening of the cover 13 which holds the sensor 14 with respect to the outer race 7 is tightly fitted into the inside opening of the outer race 7 in order to prevent the cover 13 from being carelessly disconnected from the outer race 7 by the vibration caused when the automobile is running.
However, when the cover 13 is tightly fitted into the outer race 7 as described above, it becomes difficult to separate both members 7, 13 from each other. When both members 7, 13 are forcibly separated from each other with a tool such as a driver, a strong force is given to the cover 13, and the cover 13 is deformed. As a result, it is impossible to use the cover 13 again. For this reason, when either the rolling bearing portion or the sensor 14 is out of order after the rolling bearing unit has been incorporated into an automobile and used over a long period of time, the entire rolling bearing unit having a rotating speed detector must be also replaced, that is, a portion which is in good order must be replaced. This causes a raise in the maintenance cost. From the viewpoint of economizing resources, such a case is not preferable.
In view of the above circumstances, in order to detach the cover 13 from the outer race 7 easily, Unexamined Japanese Utility Model Publication No. 5-14634 discloses a rolling bearing unit having a rotating speed detector as shown in FIG. 22, which is referred to the third conventional example. In the rolling bearing unit having a rotating speed detector, a flange portion 3 for fixing a wheel is formed on an outer circumferential surface of the outside end portion of the hub 1 composing a rotating wheel in conjunction with the inner race 2. An inner raceway 4a and a step portion 15 are formed on an outer circumferential surface of the middle portion of the hub 1. In the inner race 2 having the inner raceway 4b which is formed on the outer circumferential surface of the hub 1, an outside end surface of the inner race 2 is confronted with the step portion 15 so that the inner race 2 is outwardly supported to the outer circumferential surface of the hub 1.
A male screw portion 5 is formed on an outer circumferential surface of the inside end portion of the hub 1. When a nut 6 is fastened to the male screw portion 6, the inner race 2 is fixed in a predetermined portion on the outer circumferential surface of the hub 1. An irregular portion 16 is formed on an outer circumferential surface of the nut 6. Therefore, the nut 6 functions as a tone wheel for detecting a rotating speed of the nut 6. An attaching portion 8 for fixing the outer race 7 to the suspension is formed on an outer circumferential surface of the outer race 7. A pair of outer raceways 9a, 9b are formed on an inner circumferential surface of the outer race 7 and are respectively opposed to the inner raceways 4a, 4b. A plurality of rolling elements 10, 10 are installed between a pair of inner raceways 4a, 4b and a pair of outer raceways 9a, 9b so that the hub 1 can be freely rotated inside the outer race 7. A seal ring 17 is fitted between the inner circumferential surface on the outside end portion of the outer race 7 and an outer race circumferential surface of the hub 1. Further, a seal ring 17 is fitted between the inner circumferential surface on the inside end portion of the outer race 7 and an outer circumferential surface of the inner race 2. That is, the seal ring 17 exists between the inner circumferential surface of the outer race 7 and the outer circumferential surface of the hub 1, and also the eal ring 17 exists between the inner circumferential surface of the outer race 7 and an outer circumferential surface of the inner race 2. The seal rings 17 close openings on both side end portions of the space in which the plurality of rolling elements are accommodated.
A portion of the opening of the inside end portion (the right end portion in FIG. 22) of the outer race 7 is closed by a cover 18. The entire cover 18 is formed into an annular shape by press-forming a metallic sheet. The shape of the cover 18 is described as follows. In order to insert a portion of a constant velocity joint inside the cover 18 in the diametric direction, an outer periphery of the base plate portion 19 formed into an annular shape is bent at a right angle to the outside (to the left in FIG. 22), so that a cylindrical vertical wall 20 can be formed. Further, an annular step portion 21 is formed on an outer circumferential periphery of the opening of the outside end (the left end in FIG. 22) of the vertical wall 20 so that the annular step portion 21 is capable of being freely confronted with the inside end surface 7a of the outer race 7.
When an outer circumferential edge of the step portion 21 is bent outwardly at a right angle, an engaging cylindrical portion 22 capable of engaging with the inside end portion of the outer race 7 is formed. When an outside end opening of the engaging cylindrical portion 22 is bent outwardly in the diametric direction by an angle of 180, an engaging portion 23, the size in the diametric direction of which is large, is formed. The cover 18 is fixed to the outer race 7 in such a manner that the engaging cylindrical portion 22 is outwardly engaged with the inside end portion of the outer race 7, and at the same time the step portion 21 is confronted with the inside end surface 7a of the outer race 7. The engaging strength of the engaging cylindrical portion 22 and the inside end portion of the outer race 7 is determined to be a sufficiently high value so that the outer race 7 and the cover 18 can not be disconnected from each other by the vibration caused when the automobile is running. For example, an electromagnetic sensor 14 is fitted inside the cover 18 and an output of the sensor 14 is sent to a controller (not shown) via a lead wire 24.
Substantially in the same manner as that of the rolling bearing unit having a rotating speed detector shown in FIG. 21, by the above rolling bearing unit having a rotating speed detector, the wheel is rotatably held with respect to the suspension, and the rotating speed of the wheel fixed to the flange portion 3 of the hub 1 can be detected. Especially, when it becomes necessary to disconnect the cover 18 from the outer race 7 for the purpose of maintenance in the arrangement shown in FIG. 22, as shown by a chain line in FIG. 22, an inner circumferential edge of a tool 25 such as a hand press or a pulley extractor having an engaging portion of split structure is engaged with an edge of the engaging portion 23 formed in the outer circumferential edge of the outside end opening of the cover 18. When the tool 25 is displaced in a direction in which the tool 25 is separated from the attaching portion 8, that is, when the tool 25 is displaced to the right in FIG. 22, the cover 18 is separated from the outer race 7, so that the cover 18 is disconnected from the outer race 7.
In the conventional structure shown in FIG. 22, the cover 18 is formed from a metallic sheet by means of plastic working. On the other hand, when the cover is made of synthetic resin and the sensor is embedded in a portion of the cover in the process of injection molding, it is possible to reduce the manufacturing cost of the rolling bearing unit having a rotating speed detector. This structure is conventionally known, in which the sensor is embedded in a portion of the cover made of synthetic resin. For example, European Patent Publication No. EP0557931-A1 discloses the above arrangement. This arrangement shown in FIG. 23, which is defined as the fourth conventional example, is described as follows. A sensor 20a is embedded in the cover 18a made of synthetic resin which closes an inside end opening of the outer race 8. Onto an outer circumferential surface of the opening end portion of the cover 18a, a sleeve 31 is fixed, which is formed from a metallic sheet such as a steel sheet having a sufficiently high rigidity, and the section of the sleeve 31 is an L-shape and the entire shape of the sleeve 31 is formed into an annular shape.
When the sleeve 31 is set in a cavity of the mold in the process of injection molding of the cover 18a, it can be embedded in the above synthetic resin. The above cover 18a is fixed to the outer race 8 when the above sleeve 31 is inwardly engaged with an inside end opening of the outer race 8. Compared with the arrangement shown in FIGS. 19 and 20 into which the cover formed from a metallic sheet is incorporated, this arrangement into which the above cover 18a made of synthetic resin is incorporated is advantageous in that the number of components can be reduced so that the combining work can be simplified and the manufacturing cost of the bearing unit can be lowered, and further the cover made of synthetic resin can be made lighter than the cover made of metal.
However, even in the rolling bearing unit having a rotating speed detector shown in FIG. 23, the following problems to be solved may be encountered. When an automobile is running in a rainy day, muddy water is splashed on the cover 18a and the outer race 8, and further in the case of washing an automobile, water is sprayed on the cover 18a and the outer race 8 with high pressure by a washing machine. In this case, both muddy water and washing water are referred to as muddy water hereinafter. When the muddy water enters the cover 18a and the outer race 8, not only the durability of the bearing unit is deteriorated but also the reliability of the rotating speed detector is affected.
For example, in the conventional arrangement shown in FIG. 23, muddy water enters the cover 18a and the outer race 8 through the following two passages denoted by (1) and (2).
(1) A first minute clearance formed between an outer circumferential surface of the sleeve 31 and an inner circumferential surface of the inside end portion of the outer race 8.
(2) A second minute clearance formed between an inner circumferential surface of the sleeve 31 and an outer circumferential surface of the cover 18a made of synthetic resin.
The first minute clearance is made by minute irregularities which inevitably exist on the outer circumferential surface of the sleeve 31. That is, it is inevitable that minute irregularities of several tens .mu.m exist on the surface of the sleeve 31 formed from a metallic sheet such as a stainless steel sheet. For this reason, even when the sleeve 31 is press-fitted into the inside end opening of the outer race 8, the above first minute clearance is made, and there is a possibility that muddy water enters the bearing unit through the first minute clearance.
The above second minute clearance is made by a difference between the thermal expansion coefficient of a metal composing the sleeve 31 and the thermal expansion coefficient of synthetic resin composing the cover 18a . There is a possibility that muddy water enters the bearing unit through the second minute clearance described above.
In the case of the arrangement of the fourth conventional example shown in FIG. 23, it is difficult to assemble a bearing unit without using an exclusive press. Therefore, in a garage having no exclusive press, it is impossible to replace the sensor 20a attached to the cover 18a. As a result, when the rolling bearing unit having a rotating speed detector is inspected and repaired, the cost is raised. When the cover 18a is pulled out from the outer race 8, due to a high frictional force acting between the outer circumferential surface of the end portion of the outer race 8, an end edge (a left end edge in FIG. 23) of the sleeve 31 strongly pushes an outer circumferential portion 52 close to the fore end portion of the synthetic resin composing the cover 18a. As a result, a base of the portion 52 made of synthetic resin is given a shearing force, and there is a high possibility that the portion 52 is damaged. When the portion 52 is damaged, the cover 18a and the sensor 20a embedded in the cover 18a can not be used again, which raises the cost of inspection and maintenance.
In order to prevent the shearing force from being given to the outer circumferential portion 52 close to the fore and portion when the cover 18a is pulled out from the outer race 8, it can be considered to increase an outer diameter of the flange portion 53 formed in the base portion (the right end portion of FIG. 23) of the sleeve 31. When the outer diameter of the flange portion 53 is increased and an outer circumferential portion of the flange portion 53 is protruded from the outer circumferential surface of the cover 18a so that a tool can be hooked at this protruding portion, it is possible to prevent the occurrence of a shearing force which may cause a damage of the portion 52. However, when the outer diameter of the flange portion 53 is simply increased, muddy water sprayed onto the outer side of the flange portion 53 in a rainy day or in the process of washing an automobile tends to enter the inside of the outer race 8 through a contact surface of the sleeve 31 with the outer race 8. Therefore, it is not appropriate to adopt the above countermeasure.
In the rolling bearing unit having a rotating speed detector shown in FIG. 23 into which the cover 18a made of synthetic resin is incorporated, it is possible to reduce the initial cost. On the other hand, it is difficult to remove the cover 18a from the outer race 8 in the arrangement of maintenance and replacement of parts. When the cover 18a is forcibly removed from the outer race 8 in the arrangement shown in FIG. 23, there is a possibility that the end portion 51 of the cover 18a is damaged due to a frictional force that acts between the outer circumferential surface of the sleeve 31 and the inner circumferential surface of the outer ring 8. When a portion of the sleeve 31 and a portion of the cover 18a are outwardly protruded from the outer circumferential surface of the end portion of the outer race 8 in the diametric direction, it is possible to remove the cover 18a from the outer race 8 without damaging the cover 18a. However, when the above means is adopted for removing the cover 18a, the outer diameter of the cover 18a is increased, so that the cover 18a tends to interfere with other parts. Accordingly, the degree of freedom is deteriorated in the design of an automobile.